One of Alaska's most populated cities is bracing for potentially catastrophic flooding as a basin dammed within the Mendenhall Glacier has started to release water.

A wave of water that gushed out of an Alaskan glacial lake and sent a river surging to a new record level is causing flooding issues in the state capital of Juneau for the third consecutive August.

Update, 6:25 a.m. Wednesday: The Mendenhall River hit a record level as of 6 a.m., according to the National Weather Service. The river is in major flood stage at 16.17 feet and rising, the agency said. That surpasses the record set last year of 15.99 feet.